727 input shaft seal leaking on a fresh rebuild.

Posted By: Pat_Whalen

727 input shaft seal leaking on a fresh rebuild. - 09/14/10 01:51 PM

A couple of months ago I rebuilt my very first 727. You can imagine my surprise when it worked perfectly during a couple of road tests.

I just knew something was going to go wrong, and now my fears have been realized. After driving the truck and parking it, I'll get 5-10 drops of ATF dripping from inside the bellhousing and running down to the underside of it.

What are the odds that a brand new input seal are bad? I remember checking the torque converter hub for burrs and it was smooth, so I'm not sure if that is the issue.

I really wish I knew where I went wrong on that one, because if I'm going to pull it down to replace, It's not the most fun thing in the world to do (NP205 transfer case hanging off the back of it is heavy for just little ol' me).

Posted By: MoparforLife

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 02:02 PM

Did you put a coating of grease on the seal where the converter rides. It is not all that common but you know s*** happens. Big thing is it works right.

Posted By: scratchnfotraction

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 02:39 PM

vent hole is there above the input shaft also,just check and make sure its not over filled

when my 727 was over filled and ran real hard it would spit it out the vent

was it a good seal,I have gotten were I wount use the cheap seals,I go to the dealer and get a mopar seal for that spot for sure

drop the xfer off the back of it first would be they way to go

your right,no fun at all on a 4x4,at least you dont have to jack it up as high

with greese or dip in atf,just so its not dry on start up

good luck pat

Posted By: buildanother

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 03:36 PM

Agreed on making sure trans is not overfilled.

Posted By: Dodgem

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 03:43 PM

Quote:

Agreed on making sure trans is not overfilled. [/quote
]

the fluid expands quite a bit hot!

Posted By: 6pkaar

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 03:59 PM

Did you have the converter hanging on the input shaft since the tranny was rebuilt? I've heard the weight of it can distort the shape of the seal, then when it's installed the seal will leak.

Posted By: 74fldart

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 04:52 PM

i feel your pain, i rebuilt my 1st 727 2 yrs back and had a main seal leak from day one and i havent even driven the car yet (still a running project) but it got so bad a few weeks ago that i decided to pull the tran and replace the seal. i did skimp and use some cheap parts when i reb uilt it, so i went to carquest and got a good seal and now it doesnt leak one drop.

Posted By: John_Kunkel

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 08:51 PM

Are you saying that the fluid only drips from the bell when sitting shut off or is this just the only time you've looked?

Posted By: dOOc

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 08:56 PM

Take the dust-cover off and point the vehicle down-hill slightly and see if there is a leak then.

Posted By: Dean_Kuzluzski

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 09:04 PM

Did you change the bushing that supports the converter snout?

Edit: I think they call that the pump drive bushing? Is there a new one?

Posted By: challengermike

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 09:14 PM

did you fill it in neutral,they dont pump in park.

Posted By: Commando1

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/14/10 09:30 PM

I chased an elusive leak like forever until I found that tranny fluid was "wicking" at the front of the pan so that it looked like it was coming from the converter area. Very deceptive.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:19 AM

Thanks for all the responses, guys. I'll try and answer all the questions at once.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:20 AM

Quote:

Did you put a coating of grease on the seal where the converter rides. It is not all that common but you know s*** happens. Big thing is it works right.

No kidding. I was very surprised/happy when it actually shifted properly and doesn't appear to have any other major defects.

If memory serves me correctly, I did cover the seal in ATF, not grease. Should it have been grease? If so, what kind?

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:21 AM

Quote:

vent hole is there above the input shaft also,just check and make sure its not over filled

when my 727 was over filled and ran real hard it would spit it out the vent

was it a good seal,I have gotten were I wount use the cheap seals,I go to the dealer and get a mopar seal for that spot for sure

drop the xfer off the back of it first would be they way to go

your right,no fun at all on a 4x4,at least you dont have to jack it up as high

with greese or dip in atf,just so its not dry on start up

good luck pat

Mike,

I relocated my vent hole to the top of the case and plugged the old vent hole location. I wish it were that easy.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:22 AM

Quote:

Did you have the converter hanging on the input shaft since the tranny was rebuilt? I've heard the weight of it can distort the shape of the seal, then when it's installed the seal will leak.

Negative, converter only went on when the trans was ready to be installed. I heard about this and made a point not to do that.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:24 AM

Quote:

Are you saying that the fluid only drips from the bell when sitting shut off or is this just the only time you've looked?

If I wipe the bell clean and let it sit, no dripping.

If I start it and run it in the driveway in park, a small "stream" will form on the underside of the bell but not drip (this may be fluid left over from inside of the bell since I typically park uphill.

If I park it in the driveway after driving it and getting it up to temperature, that is when five-10 drips will appear on the ground directly under the bell, and then a small "almost drop" will form, hanging there, taunting me. Until I wipe it away and repeat the cycle.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:25 AM

Quote:

Take the dust-cover off and point the vehicle down-hill slightly and see if there is a leak then.

No dust cover installed yet.

I'll try parking it downhill today after I take it for a ride.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:26 AM

Quote:

Did you change the bushing that supports the converter snout?

Edit: I think they call that the pump drive bushing? Is there a new one?

Yes, the pump drive bushing was changed.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:28 AM

Quote:

did you fill it in neutral,they dont pump in park.

I don't want to say one way or the other. I don't recall filling it in neutral, but I do remember checking it properly after driving it around, letting it sit, put in neutral on level ground and it was full.

Posted By: Pat_Whalen

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:29 AM

Quote:

I chased an elusive leak like forever until I found that tranny fluid was "wicking" at the front of the pan so that it looked like it was coming from the converter area. Very deceptive.

I know trans leaks can be pretty deceptive. I thought my pan wasn't sealed for a while and it turned out the test port on the front servo housing didn't have it's plug tightened and it was wicking into the pan gasket area.

This one is definitely coming from the bell. If I wipe it off and watch it in drive while parked, you can see it run down from in that area.

Posted By: zzyzxpat

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 12:50 AM

Sounds like a pressure leak. Wouldn't be the first time I have seen a converter leak. If you are sure it is coming from the front, you are going to have to remove the trans. Pull the trans, remove the converter, look at the hub. What is the condition of the hub surface? It must be smoooth as a babies bottom. Look for any cracks around the pump drive slots. Remove the pump and disassemble. Look at the bushing. Any wear or roughness? If there is, the hub on the converter will have some too. Look at the seal. It should have a sharp sealing area that contacts the converter hub. If you see no reason for it to be leaking, have the converter pressure tested. Do not put it back together until you are sure you think you found the problem

Posted By: Neil

Re: 727 input shaft seal leaking on a fresh rebuild. - 09/15/10 01:17 AM

I use a thin coating of engine assembly paste on convertor snouts instead of wiping the seal with atf. The paste actually stays in place, and does a better job of lubricating the seal, imo.